Summary The Saskatchewan Government Northern Air Operations Convair 580A (registration C-GSKJ, serial number202) was conducting stop-and-go landings on Runway36 at the airport in La Ronge, Saskatchewan. On short final approach for the third landing, the aircraft developed a high sink rate, nearly striking the ground short of the runway. As the crew applied power to arrest the descent, the autofeather system feathered the left propeller and shut down the left engine. On touchdown, the aircraft bounced, the landing was rejected, and a go-around was attempted, but the aircraft did not attain the airspeed required to climb or maintain directional control. The aircraft subsequently entered a descending left-hand turn and crashed into a wooded area approximately one mile northwest of the airport. The first officer was killed and two other crew members sustained serious injuries. The aircraft sustained substantial damage. The accident occurred during daylight hours at 1245central standard time. Ce rapport est galement disponible en franais. Other Factual Information The accident aircraft, a Convair 580A (CV-580A), was one of two aircraft that had recently been delivered to the Government of Saskatchewan's Northern Air Operations. CV-580As had been converted to aerial tankers (water bombers) for fighting forest fires. The accident flight was a training flight that consisted of stop-and-go circuits at the La Ronge Airport. The purpose of the training was to instruct and cross-qualify new CV-580A captains as first officers for future training requirements. The first two circuits were unremarkable; all altitudes, speeds, and aircraft performance were as expected for the exercises being carried out. The final approach leg of the third circuit differed from the first two in that the aircraft's speed was lower. The airspeed was stabilized at 103knots indicated airspeed (KIAS). The rate of descent and respective altitudes were unstable compared with those of the first two circuits. The captain had called for a power setting of 150to 200horsepower(hp) on both engines on short final approach, and the flaps, which had been set at 24, were selected to 28. The aircraft entered a high sink rate of approximately 1280feet per minute (fpm). In an effort to arrest the high sink rate, the captain, who was the pilot flying (PF), called for increased power, briefly increased pitch attitude, and then touched down on the runway, approximately 200feet beyond the threshold. The first officer, the pilot not flying (PNF), responded to the captain's call for power by rapidly advancing both power levers to a point beyond the maximum power setting limit. When the power levers were advanced, the left propeller immediately autofeathered and the left engine shut down. The captain, noting the position of the power levers, quickly retarded them to a position he assumed would give maximum power. During the final approach leg and on the go-around, the captain was not continuously setting or monitoring the engine power settings and consequently was unaware of the engine power or the nature of the emergency. The elapsed time between encountering the high sink rate and initiating the go-around was approximately seven seconds. After touching down on the runway, the captain, believing that the aircraft was not aligned with the runway, initiated a go-around. The runway heading in La Ronge is 357 magnetic(M), and, at the point where the go-around was commenced, the aircraft's heading was 356M. The autofeather was not called out or identified as an emergency. The decision to go around was not called out or communicated to the first officer. The actions taken to perform the go-around were sequentially as follows: the go-around was commenced at an airspeed of approximately 94KIAS (V1minus2)1 the gear was selected up during a momentary positive rate of climb; and the flaps were retracted at an airspeed of 95KIAS, after the aircraft cleared the very high frequency omnidirectional radio range (VOR) transmitter located left of the departure end of Runway36. Shortly after the aircraft became airborne, its left wing dropped slightly and could not be righted. The airspeed fluctuated between 93and 98KIAS and would not increase with a positive pitch angle. Once the flaps were retracted at 95KIAS, the angle of bank increased uncontrollably. The aircraft started to descend, and collided with trees and terrain in a wooded area on the airport property. There were indications that, sometime after the loss of control, the first officer pulled the left Ehandle.2 The Flight Crew There were three pilots on board C-GSKJ. A contract training captain, who was employed by Conair Aviation (Conair),3 was flying from the left seat. The captain was instructing the first officer in first officer duties. The first officer and the third pilot (occupying the centre observer's seat) were newly qualified Saskatchewan Government Northern Air Operations CV-580A captains. The pilot occupying the centre observer's seat was to take a turn at flying from the right seat later in the flight. All three pilots held valid Canadian airline transport pilot licences, the appropriate instrument ratings, and endorsements for the Convair 580. The captain had 9500hours of total time and 750hours on type. The first officer had 13000hours of total time and 25hours on type. The pilots were adequately rested and fit in accordance with company and Transport Canada medical Category1 requirements. All crew members appeared fit and capable of performing their duties on the day of the accident. Weather The weather observation for the La Ronge Airport at 1300 central standard time4 was as follows: wind 040at 10knots, few clouds at 5000feet, few clouds at 6000feet, few clouds at 9000feet, temperature 13C, dew point 2C, altimeter setting30.42. The runway was bare and dry. Weather conditions of this type do not normally produce windshear. Company Standard Operating Procedures The reference and training documents available to the crew that contained CV-580A standard operating procedures (SOPs) were as follows: a copied and non-current version of the Conair aircraft operating manual (AOM)- all Saskatchewan government pilots had been provided with a copy of this manual; a current and reformatted Conair AOM; Conair's SOP revision 06/03/25; and a quick reference handbook (QRH) on board the aircraft. It could not be determined which SOPs were in use by the crew of C-GSKJ. The profile chart on page 4-19 of the current Conair AOM directs crews to approach at an airspeed of 120 knots, for the final approach fix (FAF) to runway threshold segment of the approach. However, the expanded description of "Stabilized Approach Factors" on page 4-15 suggests that the aircraft should be stabilized at Vref+10 by 500to 800feet above ground level (agl) for a straight-in approach or by 300feet agl on a circling approach.5 Normal engine power to achieve a straight-in approach would be approximately 500 hp per side. The QRH did not contain any information concerning go-around procedures. Conair's current CV-580A AOM (Section3.28.6, page86) directs pilots to apply maximum except take-off (METO) power (971TIT6) in the event a go-around is required. The Training & Flight Profile section of that manual (sections4.13.2 and 4.13.4) directs pilots to apply maximum power (1071TIT or 4000hp per side). The actions specified for a single engine go-around (after the power is increased) are as follows: rotate to overshoot climb attitude ( approximately 8 to 10 nose up to achieveV2)7 select flaps to 15 select landing gear up (upon achieving a positive rate of climb) If there is a malfunction or emergency during the take-off that requires a rejection, a reject can be performed up to the V1 speed; at or above this speed, the take-off must be continued. The V1 speed for C-GSKJ at the time of the occurrence was 96KIAS. The go-around was attempted from a speed of 94KIAS. There was no information available in any of the AOMs that provides direction or cautionary information with respect to executing a rejected landing, unwarranted autofeather activation, or undesired negative torque system activation. Neither the normal or abnormal checklists have a section for training in the circuit. During circuit training, the crew's workload is increased substantially as the time available to carry out required cockpit duties is less than the time available during normal arrivals or take-offs. The after-take-off checklist directs the crew to disarm the autofeather system. The approach and landing checklists did not specify any action with respect to autofeather status. Often, when simulating engine failures, at lighter take-off weights, training pilots will reduce power on the operating engine to avoid exceeding gear and flap limitation speeds and to simulate higher gross weights. Aircraft Flight Data C-GSKJ was equipped with a "Chelton Flight Logic" electronic flight information system (EFIS). Aircraft approach profile data retrieved from the aircraft's EFIS were correlated with radar information, which enabled the production of a video flight recreation. The resulting information indicated that the aircraft's airspeed on the final approach was substantially lower than it had been on the previous two final approaches. On this third approach, the aircraft's speed had been established at a speed of 103KIAS for approximately five miles before the runway threshold. The data for the last part of the third approach showed that the aircraft descended rapidly below the normal approach path to near ground level, and then lost airspeed at the time the crew arrested the rapid descent. The recovery was consistent with flight in a low-energy condition. At an airspeed of 95KIAS and landing weight of less than 40000pounds, the runway length required for C-GSKJ to land and stop was approximately 4100feet.8 At the point where the aircraft touched down, approximately 200feet from the threshold, there was 4750feet of runway remaining. The horsepower gauge for the right engine was indicating large fluctuations shortly before the aircraft crashed. Wreckage Information Inspection of the wreckage revealed the following relevant information: oil tank valve was found closed; fuel valve was found closed; left propeller was feathered; left feathering button "In"; and left E handle pulled. oil tank valve was found closed; fuel valve was found closed; left propeller was feathered; left feathering button "In"; and left E handle pulled. incurred greater damage than the left engine due to impact forces. the four 10th stage bleed valves were found open, and the four 5th stage bleed valves were found in an intermediate position. incurred greater damage than the left engine due to impact forces. the four 10th stage bleed valves were found open, and the four 5th stage bleed valves were found in an intermediate position. Both engines and propellers were removed and sent to an overhaul facility for complete teardown inspection. Apart from superficial impact damage, the left engine was in running condition and was later run in an engine test cell. The engine was found to be in serviceable condition with no pre-impact anomalies. The condition of the left engine was consistent with an engine that had been shut down either through activation of the autofeather system or by the manual selection of the Ehandle. Teardown and inspection of the right-hand engine indicated the following: reverse blade bending of the first stage compressor; compressor displayed light ingestion of vegetation; re-solidified metal spatter on the 1st stage power turbine vanes, blades, and thermocouples; internal coordinator impact mark correlating to a 68 coordinator position;9 all engine components were bench tested and no pre-impact anomalies were noted; teardown of the right engine did not reveal any pre-impact anomalies; teardown of the right propeller revealed blade angles at 53 to 54 degrees; and the damage to the right engine was indicative of an engine running at a low power setting or one that was in the process of shutting down. An examination of the aircraft flight controls indicated the following: all flight controls were inspected and no pre-impact anomalies were found; both flap gear boxes were found in a position that corresponded with an 8flap setting at the time of impact; flap torque differential cutout switches were found centred and neither switch was made, indicating no flap asymmetry at the time of impact; all feather relays and associated wiring were tested for continuity and no anomalies were found; and the left E handle was pulled out. Autofeather System The CV-580A aircraft is equipped with an autofeather system that provides anti-drag protection in the event of an engine failure during critical flight phases. The system functions by detecting actual low propeller thrust. This autofeather system is a "committed" type in that it is committed to fully feathering the propeller and shutting down the engine when the following conditions are met: the pedestal-mounted autofeather switch is in the Arm position; the power lever is advanced beyond the 60 (65 coordinator) position; and the thrust sensitive switch detects less than 500pounds of propeller thrust. This committed type of autofeather system does not incorporate a timed delay; such a device would allow for transient propeller thrust during engine "spool-up." Testing of a similarly equipped aircraft revealed that it is possible to induce an unwarranted activation of the aircraft's autofeather system by rapidly advancing the power levers when the propellers are in a low-thrust condition. When an operating engine is autofeathered and shut down, the aircraft initially yaws as the propeller blade angle increases toward feather, and then yaws in the other direction as the drag decreases. The resulting control forces are remarkably different from those felt from an actual engine failure, and could tend to confuse the crew as to the asymmetric nature of the emergency. Negative Torque and Temperature Datum Systems The CV-580A is equipped with a negative torque sensing (NTS) system to provide engine negative torque (engine overspeed) protection, during periods of temporary fuel interruption, air gust loads, or power loss. The system functions by measuring negative torque values in the engine reduction gearbox and increases propeller blade angle by overriding the propeller governor whenever a negative torque value of minus 230hp to minus 320hp is detected. Engine turbine inlet temperature (TIT) is controlled by power lever position and through a fuel trimming system also known as the temperature datum (TD) system. The TD system has the capability to limit and control TIT. The TD system limits TIT to values below 1077 whenever the power lever is beyond the 60 (66 coordinator) position and engine rpm is greater than 13000 (94percent). The TDsystem limits TIT to values below 830 during engine start, acceleration up to 94percent, and operation in low-speed ground idle. The TD system controls TIT to a power lever-established value when engine speed exceeds 13000rpm and power lever position is greater than 66. If the system is operating normally, it is not possible to exceed engine temperature limits. Information provided by propeller system consultants and the Convair type certificate holder indicated that it is possible to induce undesired activation of the NTS system through a rapid advancement of the power lever followed by a quick retardation. This type of power lever movement could result in inertial propeller forces conflicting with the TD system mode in unusual flight regimes. An undesired NTS activation at low airspeed could cause the engine to under speed and flame out. Flight Characteristics Shortly after the occurrence, the Saskatchewan Government, in conjunction with TSB investigators, conducted a flight in a similarly equipped CV-580A. Several single engine go-around procedures were simulated in different aircraft configurations. In summary, the results were as follows: When a go-around was carried out from an airspeed greater than V2and as directed in the AOM (maximum power, flaps 15, positive rate, gear up), a successful go-around was achieved. When a go-around was attempted by retracting the landing gear first, with the right engine power set at the 28 coordinator position, and the flaps remaining at 24, the aircraft would not accelerate toV2, and a steady positive rate of climb could not be achieved. Aircraft control was maintained. When a go-around was attempted with flaps 24, airspeed at 94KIAS, in a 5 bank in a left turn, a positive rate of climb could not be achieved. Directional control was barely manageable with the flaps at 24, but was lost when the flaps were retracted; the angle of bank increased, and the aircraft eventually entered an incipient spin. With both engines operating and set to 100hp per side, each time the power levers were rapidly advanced at a stabilized airspeed of 105KIAS, an unwarranted autofeather was induced.